The present invention relates to an electrophotographic photosensitive body used for electrophotographic printers, copiers, and facsimile machines as well as to a manufacturing method for this photosensitive body. In particular, the present invention relates to an electrophotographic photosensitive body that is highly stable due to an improved additive for a charge-transporting layer, containing a charge-transporting material; and to a corresponding manufacturing method.
An electrophotographic photosensitive body must be capable of holding surface charges in a dark place and of generating or transporting these charges when exposed to light. Single-layer photosensitive bodies have all these functions in a single layer. Laminated photosensitive bodies are made up of a stack of laminated layers, each having separate functions. These laminated layers include a layer mainly contributing to the generation of charges and a layer mainly contributing to the retention of surface charges in a dark place and the transportation of charges on reception of light.
Image formation based on an electrophotographic process using such an electrophotographic photosensitive body uses, for example, the Carlson process. Image formation based on this process charges a photosensitive body in a dark place by means of corona discharge, forms an electrostatic latent image such as characters from a manuscript or a picture on the surface of the charged photosensitive body, develops the electrostatic latent image using toner, and transfers and fixes the developed toner image onto a support such as paper. After the toner image has been transferred, the photosensitive body is subjected to static charge erasing, residual-toner removal, and static recharge in preparation for reuse.
Conventional photosensitive materials for electrophotographic photosensitive bodies described above include either inorganic or organic photoconductive materials. The inorganic or organic photoconductive materials are diffused in a binder resin. The organic photoconductive material may be deposited by vacuum-evaporation or sublimation. Examples of inorganic photoconductive material include selenium, selenium alloys, zinc oxide, or cadmium sulfide. Examples of organic photoconductive materials include poly-N-vinylcarbazole; 9,10-anthracenediolepolyester; hydrazone; stilbene; butadiene; benzidine; phthalocyanine; or a bis azo compound.
It is also known that various additives are added as required to improve electrophotographic characteristics. For example, a salt composed of only a metal ion and an aromatic carboxylic acid is known as an additive for a charge transporting layer. This is described in, for example, Japanese Patent Application Laid Open No. 3-78753.
A zinc salt composed of only an aliphatic carboxylic acid is also known and described in, for example, Japanese Patent Application Laid Open No. 4-296867. Furthermore, the addition of a zinc salt composed of two or more types of aliphatic carboxylic acids is disclosed in Japanese Patent Application Laid Open No. 4-296867 despite an absence of descriptions of embodiments. As described above, various additives used to improve the electrophotographic characteristics of an electrophotographic photosensitive body have been examined, but their long-term stability, especially the stability of the residual potential during repeated use, has not been sufficiently improved. That is, the effect of an additive such as a zinc salt composed of an aromatic or aliphatic carboxylic acid in contributing to the stability of an electrophotographic photosensitive body and a coating liquid is insufficient, and its effects on stability have not been clarified.